What's a good first brand new car for a young adult?

I assume that would be a personal choice regardless of age. My opinion is choosing a car has nothing to do with age. For example myself, doesn't matter if it be 10 years old or 100 years old, I only love American muscle car specially the old ones. I  don't actually like "brand new" cars at all. So it's my own preference regardless of age. I guess that works for everyone.

Any model from Nissan, Toyota, Honda, Subaru, Volvo, Hyundai. American auto makers are not known for manufacturing well built, safe and reliable auto's.

Being a ex mech you want reliability  Toyota Subaru Honda

Cars are all about personal taste and choices to most people. Some people ignore certain things just because they like a look or feel of a particular car. I mean I wouldn't suggest a Mini Cooper to you, even though I absolutely love it.

I always recommend a used car. But my guess is that you've probably been driving one and as an adult you wish to buy a  brand new vehicle. It's one of those exciting moments, buying your first brand new car and I totally get that.

In the modern day, I highly recommend a hatchback. Not just any hatchback, but hot hatches. These are fun to drive, extremely fun to drive in fact. But still have the utility and space to raise a family. It allows you to enjoy your daily commute, while also being able to go on the track during the weekends or speed down a winding hill.

Ford Focus ST/ Fiesta ST. Pretty much hands down currently the best bang for your buck.

If you want to be more mature and a bit more refined, Than a Golf GTI would be your next best choice.

One that gets them from Point A to Point B reliably, while having enough room for shopping.